Cycloalkyl aminothiocarbonyl disulfides

ABSTRACT

CYCLOALKYL AMINOTHIOCARBOXYL DISULFIDES OF THE FORMULA   R-S-S-C(=S)-N(-A)-B   WHEREIN   -N(-A)-B   IS AN AMINO RADICAL IN WHICH A AND B INDEPENDENTLY ARE ALKYL, CYCLOALKYL, OR ARALKYL OR TOGETHER WITH THE NITROGEN ATOM FORM A HETEROCYCLE, AND R IS CYCLOALKYL ARE PREPARED BY REACTING CARBON DISULFIDE WITH THE APPROPRIATE SULFENAMIDE. THE NEW DISULFIDES ARE EXCELLENT VULCANIZATION ACCELERATORS.

United States Patent 3,732,222 CYCLOALKYL AMINOTHIOCARBONYL DISULFIDES Eiichi Morita, Copley, Ohio, assignor to Monsanto Company, St. Louis, M0. N0 Drawing. Filed Sept. 28, 1970, Ser. No. 76,277 Int. Cl. C07d 87/46 U.S. Cl. 260-2471 6 Claims ABSTRACT OF THE DISCLOSURE Cycloalkyl aminothiocarbonyl disulfides of the formula is an amino radical in which a and b independently are alkyl, cycloalkyl, or aralkyl or together with the nitrogen atom form a heterocycle, and R is cycloalkyl are prepared by reacting carbon disulfide with the appropriate sulfenamide. The new disulfides are excellent vulcanization accelerators.

This invention relates to methods of accelerating the vulcanization of vulcanizable elastomers. More particularly, the invention relates to cycloalkyl aminothiocarbonyl disulfides which possess special properties and to methods for preparing them.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION In accordance with this invention, cycloalkyl aminothiocarbonyl disulfides are prepared which have the formula s a I R- s s C-N\ wherein /&

is a secondary amino radical in which a and b independently are alkyl, cycloalkyl or aralkyl or together with the nitrogen atom form a heterocycle and R is cycloalkyl by reacting carbon disulfide with Branched and unbranched alkyl radicals of 1 to 12 carbon atoms are suitable for a and b. Lower alkyl radicals of 1 to 5 carbon atoms are preferred. Examples of alkyl radicals are methyl, ethyl, propyl, isopropyl, nbutyl, sec-butyl, iso-butyl, tert-butyl, amyl, hexyl, octyl, decyl and dodecyl.

Cycloalkyl radicals of 5 to 12 carbon atoms are suitable for a, b or R in the practice of this invention with cycloalkyl radicals of 5 to 8 carbon atoms being a preferred subgroup thereof. Examples of cycloalkyl radicals are cyclopentyl, cyclohexyl, cyclooctyl, cyclodecyl and cyclododecyl. Where one or both of a and b is aralkyl, radicals of 7 to 10 carbon atoms are preferred, examples of which are benzyl, phenethyl and alpha,alpha-dimethyl benzyl.

Where a and b together with the nitrogen atom to which they are joined form a heterocycle, it is preferred that it contain at least 4 carbon atoms. By heterocycle in the general formula it is meant that compounds of the formula N- (plperazinyl) are obtained.

The method for preparing the disulfides of this invention comprises reacting carbon disulfide with a sulfenamide. The carbon disulfide molecule inserts between the S-N bond of the sulfenamide forming an aminothiocarbonyl disulfide. They may be prepared in conventional manner by reacting a cycloalkyl sulfenyl halide with an alkali metal or tert-amine salt of a dithiocarbamic acid but one advantage of the new method is the elimination of the use of sulfenyl halides which are difficult to prepare and handle. The sulfenamide intermediate is con veniently prepared by the known procedures.

Cycloalkyl aminothiocarbonyl disulfides are excellent accelerators for the vulcanization of rubber. They cure faster yet have scorch properties comparable to delayedaction sulfenamide accelerators. These and other advantages of this invention shall become apparent as the description of the invention proceeds.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To form the aminothiocarbonyl disulfides by reacting carbon disulfide with the appropriate sulfenamide, the reaction may be carried out between 0-100 C. with or without an inert solvent. Good yields of disulfide are obtained by mixing carbon disulfide and sulfenamide at room temperature for 24 hours but the reaction time may be shortened by heating the mixture. Suitable solvents are ethyl ether, methanol, ethanol, chlorofrom, benzene,

heptane, hexane and ethyl acetate. In the absence of solvent, excess carbon disulfide may be used as the reaction medium. Sulfenamides suitable for the practice of this invention have the formula 8 R-SN wherein a, b and are the same as previously described.

The use of equal molar quantities of carbon disulfide and sulfenamide reactants are recommended, although the disulfides may be prepared with excess of either reactant. An excess of carbon disulfide is preferred to assure complete conversion of the sulfenamide. Of course, in the case of bis-sulfenamides, two moles of carbon disulfide for each mole of sulfenamide is reuired for complete conversion to bis(disulfide).

Example 1.Cyclohexyl piperidinothiocarbonyl disulfide To a stirred solution of N-(cyclohexylthio)piperidine 39.9 grams (0.2 mole) in 100 ml. of methanol is added with stirring in one portion 19 grams (0.25 mole) of carbon disulfide. The temperature of the reaction mixture rises from 23 to 45 C. in ten minutes. The stirred mixture is heated at reflux for 4 /2 hours and then cooled to 0 C. and held for 1 hour between 0 to 10 C. The product is recovered by filtration and air dried at room temperature. 52 grams (94.4% yield) of product is recovered. The cyclohexyl piperidinothiocarbonyl disulfide recrystallized from heptane melts at 75-76 C. Analysis gives 52.49% carbon, 7.75% hydrogen, 5.14% nitrogen and 35.10% sulfur compared to 52.31% carbon, 7.68% hydrogen, 5.08% nitrogen and 34.92% sulfur calculated for C H NS The molecular weight determined in benzene 40 is 285.

Example 2.-Cyclohexyl morpholinothiocarbonyl disulfide The procedure of Example 1 is followed except 19.0 grams of carbon disulfide is reacted with 40.3 grams of N-(cyclohexylthio)morplioline. 49 grams (88.3% yield) of disulfide is obtained. Twice recrystallized from alcohol, the cyclohexyl morpholinothiocarbonyl disulfide melts at 59.0-59.5 C. Analysis gives 47.43% carbon, 6.87% hydrogen, 5.07% nitrogen, 6.10% oxygen and 34.51% sulfur as compared to 47.61% carbon, 6.90% hydrogen, 5.05% nitrogen, 5.77% oxygen and 34.67% sulfur calculated for C H NOS The molecular weight determined in dimethylformamide is 272.

Example 3.Cyclohexyl 4-pipecolinethiocarbonyl disulfide The disulfide is prepared by the procedure of Example 1 by adding 0.14 mole of carbon disulfide to 0.11 mole of N (cyclohexylthio)pipecoline. 24 grams (75.4% yield) of disulfide is obtained. Recrystallized from heptane, the product melts at 44 C. Analysis gives 54.13% carbon, 7.89% hydrogen, 4.82% nitrogen and 33.38% sulfur compared to 53.93% carbon, 8.00% hydrogen, 4.84% nitrogen and 33.23% sulfur calculated for C H NS Example 4.Cyclohexyl 3-azabicyclo[3.2.2]non- 3-ylthiocarbonyl disulfide grams (79.2% yield) of disulfide is obtained by the procedure of Example 1 by reacting 9.5 grams of carbon disulfide with 24 grams of 3-(cyclohexylthio)-3-azabicyclo[3.2.2]nonane. Recrystallized from heptane, the disulfide melts at 104-105 C. Analysis gives 56.92% carbon, 7.87% hydrogen, 4.34% nitrogen and 30.41% sulfur compared to 57.09% carbon, 7.99% hydrogen, 4.44% nitrogen and 30.48% sulfur calculated for C H NS Example 5.Cyclohexyl 1-pyrrolidinylthiocarbonyl disulfide 19 grams of carbon disulfide is reacted with 37.0 grams of 1-(cyclohexylthio)pyrrolidine to give 40 grams (76.5% yield) of disulfide which melts at 38-39 C. when recrystallized from heptane. Analysis gives 50.39% carbon, 7.39% hydrogen, 5.48% nitrogen and 36.99% sulfur compared to 50.53% carbon, 7.32% hydrogen, 5.36% nitrogen and 36.79% sulfur calculated for C H NS Example 6.Cyclohexyl 2,6-dimethylmorpholinothiocarbonyl disulfide 49 grams (80.2% yield) of disulfide is obtained by reacting 19 grams of carbon disulfide with 45.9 grams of 4- (cyclohexylthio)-2,6-dimethylmorpholine. The disulfide melts after recrystallization from heptane at 64-65 C. Analysis gives 51.27% carbon, 7.64% hydrogen, 4.43% nitrogen, 5.23% oxygen and 31.33% sulfur compared to 51.10% carbon, 7.59% hydrogen, 4.58% nitrogen, 5.24% oxygen and 31.49% sulfur calculated for C H NOS Example 7.Cyclohexyl hexahydro( 1H) azepin- 1- ylthiocarbonyl disulfide Carbon disulfide, 20.8 grams (0.3 mole), is added to a stirred solution of 49.1 grams (0.23 mole) of l-(cyclohexylthio)hexahydro(1H)azepine in ml. of methanol. Within 3 minutes of addition, the reaction temperature rises from 27 to 48 C. The reaction mixture is heated at reflux between 55 and 61 C. for 4 hours and then cooled to room temperature and held with stirring for 24 hours. The methanol and the excess carbon disulfide is removed in vacuo at a maximum temperature of 80-90 C. at 1-2 mm. pressure. 59 grams of a viscous liquid (88.6% yield) is obtained. Refractive Index is Analysis gives 8.14% hydrogen and 4.43% nitrogen compared to 8.00% hydrogen and 4.84% nitrogen calculated for C13H23NS3- Example 8.-Cyclohexy1 N,N-diethylthiocarbamyl disulfide To a solution containing 37.9 grams (0.2 mole) of sodium N,N-diethyldithiocarbamate hydrate in 800 ml. of ethyl ether is added dropwise 0.2 mole of cyclohexylsulfenyl chloride in ml. of hexane in 20 minutes at 010 C. The reaction mixture is stirred at 2530 C. for 24 hours after which there is added 200 ml. of water and the mixture stirred for an additional 15 minutes. The ether layer is separated, washed with water until neutral, and dried over sodium sulfate. The ether-hexane solvent is removed in vacuo at a maximum temperature of 80 C. at 1-2 mm. pressure. The residue is filtered to remove a small amount of solid material. 44 grams 83.5 yield) of a viscous liquid is obtained having an index of refraction of N =1.5938. Analysis gives 49.90% carbon, 8.15% hydrogen, 5.13% nitrogen and 36.27% sulfur compared to 50.14% carbon, 8.03% hydrogen, 5.32% nitrogen and 36.51% sulfur calculated for C H NS Example 9.Cyclohexyl hexahydro(2H)azocin-1- ylthiocarbonyl disulfide 'Ihe disulfide is prepared by the procedure of Example 8 by reacting cyclohexyl sulfenyl chloride with the dithiocarbamic acid derived from heptamethyleneamine, carbon disulfide and triethylamine. 61 grams (80.4% yield) of a viscous liquid is obtained. Analysis gives 4.62% nitrogen and 31.85% sulfur compared to 4.61% nitrogen and 31.69% sulfur calculated for C H NS Example 10.Cyclooctyl 3-azabicyclo[3.2.2]non-3- ylthiocarbonyl disulfide 8.4 grams (0.11 mole) of carbon disulfide is reacted 'Wlth 23 grams (0.086 mole) of 3-(cyclooctylthio)-3- azab1cyc1o[3.2.2]nonane in 75 ml. of methanol by the procedure of Example 1. 18 grams (60.9% yield) of the desired disulfide is obtained which melts at 7l72. C. when recrystallized from heptane. Analysis gives 4.02% nitrogen and 27.96% sulfur compared to 4.08% nitrogen and 28.00% sulfur calculated for C H NS Example 1l.Cyclododecyl 3-azabicyclo[3.2.2]non-3- ylthiocarbonyl disulfide 3.8 grams (0.05 mole) of carbon disulfide is reacted with 11.3 grams (0.0349 mole) of 3-(cyclododecylthio)- 3-azabicyrlo[3.2.2]nonane in 50 ml. of methanol by following the procedure of Example 1. 10 grams (71.7% yield) of the desired disulfide is obtained which when recrystallized from heptane melts at 1l9-120 C. Analysis gives 3.32% nitrogen and 23.96% sulfur compared to 3.50% nitrogen and 24.07% sulfur calculated for C21H37NS3.

Example 12.-Cyclohexyl N,N-dimethylthiocarbamyl To a stirred slurry containing 89.6 grams (0.5 mole) of sodium N,N-dimethyldithiocarbamate hydrate in 600 ml. of ethyl ether there is added dropwise 0.5 mole of cyclohexylsulfenyl chloride in 230 ml. of hexane in one hour at 0-l0 C. The reaction mixture is stirred at 25 30 C. for 24 hours after which there is added 300 ml. of water and the mixture stirred for an additional minutes. The ether layer is separated, washed with water until neutral and dried over sodium sulfate. The etherhexane solvent is removed in vacuo. 97 grams (84.2% yield) of a low melting solid is obtained which, upon recrystallization from 100 ml. of heptane and 25 ml. of isopropyl alcohol, gave 44 grams of the desired disulfide, melting point 6262.5 C.

The accelerators of this invention are applicable to rubber stocks containing sulfur or sulfur-containing vulcanizing agents. For the purposes of this invention sulfur vulcanizing agent means elemental sulfur or a sulfur containing vulcanizing agent, for example, an amine disulfide such as 4,4'-dithiomorpholine or a polymeric polysulfide. The accelerators of this invention may also be used in comjunction with other accelerators, for example the aromatic thiazole accelerators which include benzothiazole-Z-monocyclohexyl sulfenamide, 2-mercaptobenzothiazole, 2,2'-dithiobisbenzothiazole, N-terbutyl Z-benzothiazole sulfenamide, 2-benzothiazolediethyldithio carbamate and 2-morpholinothiobenzothiazole. The accelerators may also be used with amine salts of mercaptobenzothiazole, for example the tert-butyl amine salt of mercaptobenzothiazole or salts of morpholine and 2,6-dimethylmorpholine. The accelerators are also effective with stocks containing other types of accelerators, for example the tetramethylthiuram disulfide, tetramethylthiuram monosulfide, aldehyde amine condensation products, thiocarbamyl sulfenamides, thioureas, metal dithiocarbamates, alkyl dithiocarbamates, hexamethylenetetramine, xanthates, and guanidine derivatives may also be used. The accelerators are also effective when used in combination with prevulcanization inhibitors, for example N-(cyclohexylthio)phthalimide or cyclohexylthiomorpholine. The rubber mixes of this invention may also contain antidegradants, for example N-1,3-dimethylbutyl- N-phenyl-p-phenylenediamine, N,N' bis 1,4-dimethylpentyl-p-phenylenediamine and other phenylenediamines.

The accelerators of this invention give improved results in rubber stocks containing natural rubber and synthetic rubbers or mixtures thereof. Synthetic rubbers which may be used in the process of this invention include cis-4-polybutadiene, butyl rubber, ethylene propylene terpolymers commonly called EPDM, polymers of 1,3-butadiene, for example 1,3-butadiene itself and of isoprene, copolymers of 1,3-butadiene with other monomers, for example styrene, acrylonitrile, isobutylene and methylmethacrylate. Other types of elastomers other than diene rubbers just mentioned which are improved by the accelerators of this invention are any of the sulfur vulcanizable elastomers which class includes chloroprene rubber and sulfur vulcanizable urethane rubber. Diene rubbers are preferred and elemental sulfur is the preferred vulcanizing agent.

The quantity of the accelerator varies in accordance to the application to which the vulcanizable composition is directed. However, usually the quantities are the same as commonly used for other accelerators. Normally 0.5 to 5 parts accelerator per parts elastomer is adequate. However, in certain applications, particularly when used in conjunction with other accelerators, smaller amounts will be sufficient.

The cure characteristics of the stocks are determined at the indicated temperature of a Monsanto Oscillating Disk Rheometer. The time, t required for a rise of two Rheometer units above the minimum reading and the time, 0, required to obtained 90% of the Rheometer maximum torque is recorded. The differences of the two times, t -t is a measure of the cure rate of the stocks. The Rheometer maximum torque is a measure of the state of cure or the amount of crosslinking which has taken place during vulcanization and is related to the modulus of the vulcanizate. The time required to achieve optimum cure is determined from the Rheometer data and vulcanizates are prepared by heating stocks in a press for the indicated time. The scorch properties of the stocks are determined by a Mooney Plastometer and the time, 1 in minutes for the Mooney reading to rise five points above the minimum viscosity is recorded. Longer times on the Mooney scorch test indicate greater processing safety.

To illustrate the accelerator activity of the compounds of this invention, a natural rubber masterbatch and styrene-butadiene rubber masterbatch are prepared of the following composition. All parts are by weight.

Natural Styrenerubber butadiene mastermasterbatch batch Natural rubber 100. 0 Oil-extended SB 137. 5 Furnace carbon black 45. 0 65. 0 Zinc oxide 3. O 3.0 Stearic acid 2.0 1. 0 Hydrocarbon softener 5. 0 1. 5

Total parts 155. 0 208. 0

Vulcanizable stocks are prepared by incorporating into parts of the natural rubber masterbatch 2 parts sulfur, 2 parts of a p-phenylenediamine antidegradant and 0.5 part accelerator, and into 208 parts of the styrenebutadiene masterbatch 2 parts sulfur, 2 parts of a pphenylenediamine antidegradant and 1.0 part accelerator. The accelerators in each stock tested are as follows:

10 Cyclohexyl hexahydro(2H)-azocin-1-ylthiocarbonyl disulfide 11 Cyclooctyl 3-azabicyclo [3 .2.2] non-3-ylthiocarbonyl disulfide 12 Cyclododecyl 3-azabicyclo[3.2.2] non-3-ylthiobonyl disulfide The stocks are evaluated as previously described.

nitrogen atom form a heterocycle of 4 to 8 carbon atoms and R is cycloalkyl of 12 carbon atoms.

STYRENE-B UTADIENE RUBBER STOCKS Stock 1 2 3 4 5 6 7 8 9 10 11 12 Mooney data at 135 0.: t5 20.5 22.5 21.3 24.3 25.5 17.8 25.4 15.7 18.4 18.0 24.5 25.4 Rheonietcr data at 153 NATURAL RUBBER STOCKS Stock 1 2 3 4 5 5 7 8 0 10 11 12 Mooney data at 121 0.; r5 30.5 28.1 30.8 30.5 31.0 17.4 34.0 21.7 22.0 22.0 33.0 33.2 Rlicometer data at 144 0.:

Although the invention has been illustrated by typical 9 2. A process according to claim 1 wherein the heteroexamples, it is not limited thereto. Changes and modificycle is a monocyclic six membered ring. cations of the examples of the invention herein chosen 3.Aprocess according to claimZwherein for purposes of disclosure can be made which do not a S from h s 'r't an sco e of the const1t ute departure t e p1 1 d p is N (IB S S R invention. 2?

The embodiments of the invention in which an ex- 0 b elusive P p y or Prlvllege 1S Claimed are defined a5 4. A process according to claim 2 wherein R is cycl0- follows: hexyl.

P p p f y f y amlllotlllocar- 5. A process according to claim 4 wherein the amino Q y dlsulfides fvhlch C0I11P1'1Ses Teactmg carbon dlsulfide 3O radical is selected from the group consisting of piperidino, Wlth a Sulfellamlde lower alkyl piperidino, morpholino and di(lower alkyl) a morpholino. 6. A process according to claim 5 wherein the amino radical is morpholino.

to produce a compound of the formula References Clted s a Dunbar et al.: J. Org. Chem., vol. 35, pp. 279-81 ll (January 1970).

b 40 ALEX MAZEL, Primary Examiner wherein J. TOVAR, Assistant Examiner 8 US. 01. X.R.

\ 260239 B, 239 BA, 239 R, 243 B, 268 R, 293.65, 84.3,

is an amino radical in which a and b together with the 

